自己项目中遇到的一个实际问题，想了两天总算想出来了，现在记录备忘下：

func rawModelsToTree(rawModels: [Model], rootNode: String, parentNode: String, childrenNode: String) -> [Model] {

        // 0. 创建根节点
        let rootModels = rawModels.filter { $0.pId == rootNode }

        for model1 in rawModels {
            // 1. 配置根节点
            for rootModel in rootModels {
                if rootModel.id == model1.pId {
                    rootModel.subModel.append(model1)
                }
            }

            // 2. 配置子节点
            for model2 in rawModels {
                // 2.1 之前配置过的根节点排除
                guard rootModels.contains(model1) == false && rootModels.contains(model2) == false else { continue }
                if model1.id == model2.pId { // model1是model2的父
                    model1.subModel.append(model2)
                } else if model2.id == model1.pId { // model1是model2的子
                    model2.subModel.append(model1)
                }
            }
        }
        return rootModels
    }